The present invention relates to electric current generation devices. More particularly, the invention relates to improvements in stator construction for use in conjunction with a fly wheel providing a magnetic field to coils on the stator.
Small pull-start engines, such as are typically used in residential lawn mowers, generally include one or more spark plugs powered by an ignition mechanism in which current is generated by rotation of a magnet-carrying fly wheel. The fly wheel is integrally mounted to the crank shaft, which may be rotated by a pull cord. Thus, pulling the cord turns the crank shaft, thereby turning the fly wheel and activating the ignition mechanism. Thereafter, the motor drives the crank shaft so that the ignition continues to operate.
Smaller lawn mowers include a single rotary blade directly attached to the crank shaft. Although this requires the operator to overcome the inertia of the blade in rotating the crank shaft by the pull-cord to start the engine, the extra load is typically acceptable. Larger commercial mowers, however, may have multiple rotary blades driven by the crank shaft via belts extending from the shaft. The increased inertia caused by the multiple blades may make pull starting impractical. Thus, an electric clutch may be used to selectively engage the fly wheel to the loaded portion of the crank shaft. With the clutch disengaged, the fly wheel may be easily rotated by the pull-cord to start the engine. The clutch may then be engaged to turn the blades.
The clutch is an electric device run by DC current. To provide this current, the fly wheel is constructed in an alternator configuration. Typically, the fly wheel includes an inner diameter having magnets disposed thereabout. A stator concentric with the fly wheel rotor includes a series of windings, or coils. The rotor rotates at engine speed and provides a moving magnetic field which causes current flow in the windings.
Accordingly, the stator output current depends on engine speed. That is, when the engine is running at low rpm's, the fly wheel is rotating slowly, and the current output is relatively low. As engine speed increases, however, so does the alternator current output.
If the alternator output is too low at low engine speed, the clutch will not engage, and the mower is not operable. One way to resolve this problem is to increase alternator output at low rpm's. This may be done in various ways. Unfortunately, increasing current output at low rpm's in conventional systems also increases the output at high rpm's. If the current output is too high, the clutch may fail.